Measurements of the Capillary Entry Pressure in Shale
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The work in this thesis is based on setting up equipment and establishing a testing procedure for core sample measurements of capillary entry pressure in shale. The industry faces often stability problems regarding drilling through water-wet shale, and a preferred solution have been the utilization of oil-based drilling fluid, which due to capillary forces enables the well bore pressure to be higher than the pore pressure. However, if the well bore pressure gets adequate higher than the pore pressure, the capillary forces are defeated and the drilling fluid will enter the formation causing stability problems. In order to control the drilling process, it is of considerable interest to know how much higher the well bore pressure can be before penetration occurs.Within this framework of thesis, measurement of capillary entry pressure have been examined and a testing procedure have been proposed. The capillary entry pressure was measured to be 0.38MPa for Pierre shale subjected to mineral oil.The testing procedure, which includes a saturation part, a consolidation part and a capillary entry pressure part, was tested and optimized by continuously analyzing the results and adding adjustments to the design of the next test. Mathematical formulas were developed in order to perform the saturation and the consolidation on the sample when it was subjected to oil on one side and pore fluid on the other. An important finding was the reduction of the time required to saturate the sample, which was achieved by increasing the pressure difference between the confining pressure and the upstream pressure.